The present invention relates to an electric trigger switch of the type intended for use in a hand-held power tool such as an electric drill or rotary drive tool for example.
More particularly, although not exclusively, the invention relates to an electric trigger switch with a locking mechanism enabling the trigger to be locked in ON and OFF positions.
It is known to provide locking mechanisms for power tool trigger switches. These mechanisms typically include a pushbutton enabling the trigger to be locked down in the ON position, so that there is no need for a user to keep pulling the trigger. Inadvertent depression of the trigger from the OFF position to the ON position presents a safety risk.
It is an object of the present invention to overcome or substantially ameliorate the above problem and/or more generally to provide an improved locking trigger switch for a power tool.
According to the invention, there is provided a trigger mechanism for a power tool, comprising a chassis, a trigger mounted to the chassis for movement between ON and OFF position, and an electrical switch mounted to the chassis for activation by movement of the trigger between the ON and OFF positions to close and open an electrical circuit. A locking mechanism attached to the chassis is included, that being user-activated to unlock the trigger in the OFF position and trigger-activated to release the trigger in the ON position.
Preferably, the trigger is mounted pivotally to the chassis.
More preferably, the trigger mechanism includes an activating rod extending from the trigger to the electrical switch.
In a preferred embodiment, the locking mechanism comprises a single locking member arranged to lock the trigger in both the ON and the OFF positions.
More preferably, the locking member comprises a locking pin extending through the trigger and the chassis.
Further more preferably, the locking mechanism includes a locking plate fixed to the trigger and having a slot through which the locking pin passes.
Yet further more preferably, the locking pin has a narrow shank portion and a wide shank portion, and the slot of the locking plate has a width through which the narrow shank portion can pass to permit movement of the trigger and a widening at one end through which the wide shank portion is engageable to lock the trigger in the OFF position.
It is preferred that the locking mechanism further includes a pushbutton secured to the locking pin and a spring co-acting between the pushbutton and the locking plate to bias the locking pin to lock the trigger in the OFF position and to release the trigger in the ON position.
It is further preferred that the locking pin has an end remote from the pushbutton, and the trigger has an aperture into which the head is engageable to lock the trigger in the ON position.
In a preferred embodiment, the locking mechanism includes a spring biassing the locking member to lock the trigger in the OFF position and to release the trigger in the ON position.
More preferably, the locking member comprises a locking pin extending through the trigger and the chassis, the trigger including a pair of opposed side walls embracing the chassis and through which a shank of the locking pin extends, the shank having an end engageable with one trigger wall to lock the trigger in the OFF position and an opposite end engageable with the other trigger wall to lock the trigger in the ON position.
In a specific construction, the electrical switch includes two pairs of terminals, each pair being for an individual electrical circuit that are openable and closable upon movement of the trigger.